Add consistency test for cp = dh/dT at constant P

Cantera · Jun 10, 2022 · bfb11e6 · bfb11e6
1 parent e23dddd
commit bfb11e6
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Showing 2 changed files with 23 additions and 2 deletions.
diff --git a/test/data/consistency-cases.yaml b/test/data/consistency-cases.yaml
@@ -8,14 +8,16 @@ ideal-gas-h2o2:
   - {T: 400, density: 5 g/cm^3 , X: {H2: 0.1, O2: 0.7, H2O2: 0.1}}
 
 redlich-kwong:
-  setup: {file: co2_RK_example.yaml}
+  setup:
+    file: co2_RK_example.yaml
   states:
   - {T: 300, P: 101325, X: {CO2: 0.7, CH4: 0.2, H2O: 0.1}}
   - {T: 320, P: 200 bar, X: {CO2: 0.3, CH4: 0.5, H2O: 0.2}}
   - {T: 600, P: 200 bar, X: {CO2: 0.4, CH4: 0.2, H2O: 0.4}}
 
 peng-robinson:
-  setup: {file: co2_PR_example.yaml}
+  setup:
+    file: co2_PR_example.yaml
   states:
   - {T: 300, P: 101325, X: {CO2: 0.7, CH4: 0.2, H2O: 0.1}}
   - {T: 320, P: 200 bar, X: {CO2: 0.3, CH4: 0.5, H2O: 0.2}}
@@ -106,6 +108,7 @@ nitrogen-purefluid:
   setup:
     file: liquidvapor.yaml
     phase: nitrogen
+    rtol_fd: 1e-5
   states:
   - {T: 300, P: 1 atm}
   - {T: 70, P: 1 atm}
@@ -116,6 +119,8 @@ plasma:
   setup:
     file: oxygen-plasma.yaml
     phase: discretized-electron-energy-plasma
+    known-failures:
+      cp_eq_dhdT/1: Test does not account for distinct electron temperature
   states:
   - {T: 300, P: 1 atm, X: {O2: 1.0, O2-: 1e-5, E: 1e-5}}
   - {T: 300, P: 1 atm, X: {E: 1.0}}

diff --git a/test/thermo/consistency.cpp b/test/thermo/consistency.cpp
@@ -44,6 +44,7 @@ class TestConsistency : public testing::TestWithParam<std::tuple<AnyMap, AnyMap>
             cache[key].reset(newPhase(key.first, key.second));
         }
         atol = setup.getDouble("atol", 1e-5);
+        rtol_fd = setup.getDouble("rtol_fd", 1e-6);
         atol_v = setup.getDouble("atol_v", 1e-11);
 
         phase = cache[key];
@@ -72,6 +73,7 @@ class TestConsistency : public testing::TestWithParam<std::tuple<AnyMap, AnyMap>
     size_t nsp;
     double T, p;
     double atol, atol_v;
+    double rtol_fd; // relative tolerance for finite difference comparisons
 };
 
 map<pair<string, string>, shared_ptr<ThermoPhase>> TestConsistency::cache = {};
@@ -147,6 +149,20 @@ TEST_P(TestConsistency, v_eq_sum_vk_Xk)
     EXPECT_NEAR(phase->molarVolume(), phase->mean_X(vk), atol_v);
 }
 
+TEST_P(TestConsistency, cp_eq_dhdT)
+{
+    double h1 = phase->enthalpy_mole();
+    double cp1 = phase->cp_mole();
+    double T1 = phase->temperature();
+    double dT = 1e-5 * phase->temperature();
+    phase->setState_TP(T1 + dT, phase->pressure());
+    double h2 = phase->enthalpy_mole();
+    double cp2 = phase->cp_mole();
+    double cp_mid = 0.5 * (cp1 + cp2);
+    double cp_fd = (h2 - h1)/dT;
+    EXPECT_NEAR(cp_fd, cp_mid, max({rtol_fd * cp_mid, rtol_fd * cp_fd, atol}));
+}
+
 INSTANTIATE_TEST_SUITE_P(IdealGas, TestConsistency,
     testing::Combine(
         testing::Values(getSetup("ideal-gas-h2o2")),